1. Field of the Invention:
The invention relates to a double-acting rotary drive for a control device having a fixed end position in the form of a stop, including a motor and a torque-changing gear.
2. Description of the Related Art:
Double-acting rotary drives of this kind are used in particular for actuating fittings, such as valves, slides, flaps or the like, with which flow paths are opened or closed. The end position is predetermined by the closed position of the fitting, in which the movable closure element, such as a valve plate, moves to meet a stop, namely the valve seat. As described in detail in allowed U.S. application Ser. No. 833,847, filed Feb. 26, 1986, a problem which arises is that major retaining forces are produced upon striking the stop, which must be overcome when the fitting is opened. These retaining forces may even increase further during long idle times, especially because of corrosion or the like and then may overload the normal drive. Similar problems can occur if the rotary drive is used for actuating brakes, clamping jaws, doors or the like.